I am testing a simple scenario: Having many post categories, where each category has its own posts.

I want to be able to drag&drop and reorder the categories, but also the posts within a specific category.

I want to show fully extended all the lists inside a single scrollbar.

Yes it looks like I need one reorderablelistview for all the categories so I can reorder them, and for every category another reorderablelistview for ordering the posts within that category.
PS: Moving posts to another category by dragging would be awesome too

I will provide below some code that I am trying without success:

import 'dart:math';

import 'package:flutter/material.dart';

class TmpScreen extends StatefulWidget {
  const TmpScreen({super.key});

  @override
  State<TmpScreen> createState() => _TmpScreenState();
}

class _TmpScreenState extends State<TmpScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
          title: const Row(
        children: [
          Text('Posts'),
        ],
      )),
      body: SingleChildScrollView(
        child: Container(
            height: MediaQuery.of(context).size.height,
            padding: const EdgeInsets.all(16),
            child: Column(
              children: [
                Text('All posts'),
                const SizedBox(
                  height: 36,
                ),
                Expanded(
                  child: ReorderableListView(
                      onReorder: (oldIndex, newIndex) {
                        print(
                            'Reordering post categories $oldIndex -> $newIndex');
                      },
                      children: List.generate(postsByCategory.length, (index) {
                        final postByCategory = postsByCategory[index];
                        return Column(
                          key: ValueKey(postByCategory.category),
                          children: [
                            Text(postByCategory.category),
                            Expanded(
                                child: ReorderableListView(
                                    onReorder: (oldIndex, newIndex) {
                                      print(
                                          'Reordering posts inside category ${postByCategory.category}, $oldIndex -> $newIndex');
                                    },
                                    children: List.generate(
                                        postByCategory.posts.length, (index) {
                                      final post = postByCategory.posts[index];
                                      return Text(
                                          key: ValueKey(post.name),
                                          'Post ${post.name}');
                                    })))
                          ],
                        );
                      })),
                )
              ],
            )),
      ),
    );
  }
}

final postsByCategory =
    List.generate(10, (index) => generateRandomPostsByCategory(10));

class PostsByCategory {
  final String category;
  final List<Post> posts;

  PostsByCategory({required this.category, required this.posts});
}

class Post {
  final String name;

  Post(this.name);
}

String generateRandomString(int length) {
  const String chars =
      'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
  Random random = Random();
  return String.fromCharCodes(
    Iterable.generate(
      length,
      (_) => chars.codeUnitAt(random.nextInt(chars.length)),
    ),
  );
}

Post generateRandomPost() {
  String randomPostName = generateRandomString(10);
  return Post(randomPostName);
}

PostsByCategory generateRandomPostsByCategory(int numPosts) {
  String randomCategory =
      generateRandomString(8); // Generate a random category name

  List<Post> randomPosts = List.generate(numPosts, (_) => generateRandomPost());

  return PostsByCategory(category: randomCategory, posts: randomPosts);
}

The code above does not render at all.
I can fix it to render but it just doesn’t work, the lists don’t show all the items and I don’t know how to support my use case.

Any Flutter expert can provide useful insights?